Field of the Invention
The present invention relates to an improved copper alloy for electronic instruments, in particular, to the copper alloy excellent in the strength, processibility, electric conductance (thermal conductance), corrosion resistance, heat resistance, etc., and suitable for the manufacture of miniaturized precision parts.
For electronic instruments, in particular, the leads, connectors, switches, contact springs, etc., of semiconductors [IC and transistor), Cu alloys excellent in the strength, processibility, corrosion resistance and electric conductance are required. As such alloys, Cu-Be alloy and Cu-Ti alloy are known, but these are expensive. In the case of Cu-Ni-Sn spinodal alloy, the electroconductivity is as low as less than 10% IACS and the processibility is also poor. The same things can be said of Cu-Ni-Al alloy. Moreover, although the Corson alloy, Cu-Ni-Si being representative thereof, is an alloy having both strength and electric conductance, the combination of solid solution treatment and aging is indispensable in order to obtain these characteristics, while processing steps lead to increased costs. Furthermore, this alloy has the serious shortcoming as the copper alloy for electronic instruments in that the bonding of the alloy with solder deteriorate with the lapses of time (Sn or Sn-Pb alloy) thereby adversely effecting the reliability of the product. Therefore, in U.S. Pat. No. 4,594,221, the improvement in various characteristics is intended with Cu-Ni-Si-Mg alloy which has Mg added thereto, but atmospheric melt casting is indispensable because Mg is an easily oxidizable element. This factor is the primary factor reason which further up the cost of this alloy. Further, in JP 60-43448 and JP 58-124254, Cu-Ni-Si alloy containing Sn is shown as the copper alloy for terminals, connectors and lead materials, but the alloy does not meet the required characteristics desired for use of the alloy in the stated apparatus components. More excellent strength and processibility and the improvement in various characteristics such as solderability, adhesion of plating, etc., will become necessary.
The phosphor bronze for spring being used most frequently at present has a strength of about 60 to 80 kg/mm.sup.2, but the electroconductivity is as low as 10 to 15% IACS and further there are significant defects practically in the aspects of deterioration of bonding strength with solder with the lapse of time and susceptibility to corrosion cracking. For this reason, Cu-Fe type alloys, for example C194 alloy and C195 alloy are utilized partly, but the uses are limited since the processibility is inferior due to the strength being 45 to 65 kg/mm.sup.2 or so.
Recently, the electronic instruments are in trends of miniaturization and high integration and, as the Cu alloys to be used for these, the improvement in strength and electric conductance is desired strongly. Moreover, low cost is necessary to be used in large quantities and bonding strength with solder and reliability in adhesion of plating with Sn or Sn-Pb alloy are also requested to answer to the trend of surface mounting. In order to meet such requests and replace conventional alloys, alloys with higher quality and low cost performance are necessary. Namely,
(1) An alloy should be well balanced in higher levels of strength and electroconductivity, for example, it should have the characteristics of the strength of 70 to 100 kg/mm.sup.2 and an electroconductivity of 10 to 30% IACS.
(2) The alloy should be low in the cost, for example, the alloy ingredients should be inexpensive and the manufacturing process simplified at the same time.
(3) The alloy should exhibit excellent processibility, corrosion resistance and resistance to stress corrosion cracking.
(4) The bonding strength of the alloy stable over long periods of time.
(5) The alloy should exhibit platability with Au, Ag, Ni, etc., because these metals, besides Sn and Sn-Pb alloy, are used frequently for plating in the manufacture of electronic instruments.
As a result of extensive investigations in view of this situation, a copper alloy for use in the manufacture of electronic instruments having particularly excellent strength, processibility, electric conductivity (thermal conductance), corrosion resistance and heat resistance, as well as being suitable for use in manufacturing miniaturized precision parts, in particular, lead frames, connectors, etc., of semiconductors (IC, transistor and others), is required.